I. Field of the Invention
The present invention generally relates to a system and method for controlling ventilation in a tunnel for automobiles. More particularly, the present invention relates to a system and method for controlling ventilation in the tunnel, which controls a speed of vehicles traveling in the tunnel and the density of air pollution.
II. Background and Material Information
A tunnel for automobiles is usually provided a ventilator to control air pollution inside the tunnel within a permissible range. Air pollution is caused by pollutants, such as soot and carbon monoxide (CO), which are ingredients of exhaust discharged by automobiles traveling in the tunnel. Although various methods of tunnel ventilating have been proposed, a representative method will be hereinafter described.
According to a past method, for example, as disclosed in T. Koyama et al., "Road Tunnel Ventilation Control Based on Nonlinear Programming and Fuzzy Control," Trans. IEE of Japan, Vol. 113-D, No.2, February 1993) there is a traffic counter by the roadside. A traffic volume forecasting unit employing a statistical method forecasts traffic volume in the tunnel at stated periods using a value measured by the traffic counter. A ventilation scheduling unit computes a plan value of the ventilator operation volume using the forecasted traffic volume. This plan value will be a base of ventilator operation volume in the next period.
There is also a visibility index meter (hereinafter referred to as a "VI meter") measuring the state of air pollution in the tunnel. A carbon monoxide meter (hereinafter referred to as a "CO meter") measuring CO density, and an air velocity meter (hereinafter referred to as an "AV meter") measuring air velocity in the tunnel are also provided. With a ventilation feedback control unit, a modification value of the ventilator operation volume is computed by using each value measured by the VI meter, the CO meter, and the AV meter. An operation instruction for a tunnel ventilator is determined by a harmonizing unit by harmonizing between the plan value and the modification value.
On the one hand, an automobile traveling in a tunnel produces pollutants, but on the other hand each automobile influences air velocity in the tunnel. This influence is called "ventilation by traffic". However, a ventilating capacity of the ventilation by traffic fluctuates at every moment, because the speeds of the automobiles are vary depending on each driver and are apt to fluctuate at any moment. As a result, both the air velocity and pollution density in the tunnel can fluctuate at any moment.
It is well-known that the volume of the pollutants discharged by an automobile depends on the open degree of a throttle of the automobile. Resulting from the speed fluctuations of the automobiles, the volume of the pollutants fluctuates every moment. As a result, the pollution density in the tunnel fluctuates every moment likewise.
With past approaches, such as with the method described above, and other past approaches (such as the system described in JP KOKAI 4-198599), it is very difficult to control the tunnel ventilator due to the frequent fluctuation of the pollution density in the tunnel. This is because of a mechanical restriction on starting and stopping of the ventilator, and the required time to improve the pollution density with the ventilator. Therefore, a target control value of the pollution density is usually set up on the fail-safe side. As a result, unnecessary consumption of electricity is required.